The invention will be described in the context of the manufacture of printed circuit boards (PCBs) but it will be understood that the invention is not limited to such components and may be applied to the manufacture of other kinds of devices and components useful in the manufacture or assembly of various kinds of electronic components.
PCBs are presently made in individual boards or in small panels that typically contain a series of 4 or more laminated glass fiber boards including putting tinned copper or brass foil on top of the boards, and then removing via photolithography the unwanted portions of metal foil (or alternatively using a photo additive process which keeps only the necessary portions of the ultimate traces desired) leaving behind a metal trace or traces in the desired circuit pattern laminated to the insulating board. This process involves many laminating, masking, developing and etching steps and hence is slow and costly. In addition, PCBs have to be populated with various types of components, i.e., resistors, capacitors, pin terminals, shunts, tab terminals, etc. Populating these boards with these various components, when the boards are in the form of individual or discrete panels, requires expensive conveying equipment, and complex insertion systems. Another limiting feature of present day circuit boards is that they are of necessity flat. However, many devices such as turn indicators on cars or cellular telephones, and some switches, are not flat, but rather are curved and can assume many different shapes.
U.S. Pat. Nos. 5,616,053; 5,725,392; and 5,967,841 describe various schemes for semi-continuously injection molding a strip of material, for example of plastic or of low-melting metals, by a process in which a first segment is molded in a series of axially-aligned cavities in a mold, followed by ejection of the first segment from the mold, indexing of the first segment until a trailing portion having a projecting portion with undercuts or recessed regions can be reinserted into the last mold cavity, and then when the next segment is molded a leading portion of that next segment is molded over and around the reinserted projecting portion to provide a strong interlocking structure substantially in-line with the resultant strip. The process is repeated with subsequent segments forming an elongated continuous strip of the segments. Each of the segments can have particular shapes and configurations for receiving in a later operation pins of a pin header, for example. The patents also describe adding the pins to the mold during the injection molding of each segment, so that the pins are embedded within the body of the segment just as if they had been subsequently inserted into the completed segments. The total contents of all three patents are herewith specifically incorporated by reference into this application.
An object of the invention is an improved semi-continuous molding process for molding a continuous strip of insulating material with one or more circuit traces surface molded to or surface embedded in a surface of the strip leaving the circuit traces exposed for later receiving assorted electrical components in the conventional way of mounting such components onto a circuit trace of a conventional PCB.
Another object of the invention is a continuous strip of parts or components of injection molded insulating material with surface-embedded metal traces which can be used for any purpose that requires a plastic part for separate use or for assembly into a larger structure.
In accordance with one aspect of the present invention, each segment of the strip is fabricated in a semi-continuous injection molding process as described in the referenced patents. One or more metal circuit traces are then applied to the surface of the segment before or after ejection from the mold such that the metal traces tightly adhere to the underlying insulator by being surface embedded therein. This aspect of the invention is based on the surprising discovery that the metal trace can be caused to tightly adhere to its concurrently-molded or pre-molded substrate and is not easily dislodged and thus the resultant strip of insulating material with spaced circuit traces can be further processed with automatic machinery, and subsequently separated into individual components that are the equivalent of a conventional PCB. This invention takes advantage of the superior efficiency possible from processing mutiple components while supported on or as strips on reel-to-reel automatic machinery, for example, by unreeling the strip, subjecting the strip or traces to a processing step, reeling up the processed strip, and then subjecting the strip to further operations by moving the reel to another machine or while on the same machine. The advantages of reel-to-reel processing has been described in U.S. Pat. No. 5,148,596, whose contents are also incorporated herein by reference.
In accordance with a first preferred embodiment of the invention, a strip of individual circuit traces with active sections interconnected by inactive sections can be separately stamped from a sheet of metal in continuous form, with the individual traces as well as any separated trace sections held together by one or two metal carrier strips adjacent opposite sides of the strip. Next, the carrier-supported metal strip can be implanted directly onto a molded substrate of a semi-continuous molded strip of insulating material parts. This can be accomplished by superimposing the metal strip on top of the bottom mold half containing the cavities for the insulating material parts. The molding operation surface-embeds the overlying metal strip into the just molded underlying insulating material strip. Subsequently, the continuous insulating strip with the embedded circuit traces and the carrier strip or strips can be subsequently processed to separate the individual traces as well as their active sections from their inactive sections.
As a modification of the first preferred embodiment, the metal strip can be implanted directly into the surface of a hot strip of insulating material substrates just after it exits from the mold and while the surface is still soft.
As a further modification of the first preferred embodiment, the strip of insulating material substrates, if allowed to cool after molding, can then be surface heated to soften or melt its surface, followed by the implantation step of the carrier-supported traces directly into the softened substrate surface, with the separation step following as described above.
If desired, the metal strip carriers can be removed by the same operation in which the substrates are separated. If the traces are still left with inactive connecting parts, they can also be removed at the same time from the substrate-supported traces, or in a separate operation.
In accordance with a second preferred embodiment of the invention, a flexible plastic film is provided with metal traces laid out with only the active sections of a sequence of individual trace circuits by any known process or by one of the processes described above. In this film form, the circuits cannot support the usual discrete electronic components such as ICs, resistors, and capacitors. The film is then run through the semi-continuous molding process described above in which interconnected stiffer plastic supports or housings are injection molded in strip form while the plastic film with metal traces is superimposed above the cavities causing the plastic of the film to melt into the plastic of the support or housing forming at the mold exit a strip of interconnected stiffer supports with individual circuit traces surface embedded into the supports. This support strip can then be re-reeled for further component assembly or for further processing or individually-supported circuit traces separated from the strip.
In accordance with a third preferred embodiment of the invention, an insulating material substrate, e.g., for example, of plastic, can be molded in a first stage as a strip of parts interconnected by webs as described above in the first and second preferred embodiments. The molded parts are indexed to a second stage at which is present a metal stamping die which is fed from a continuous reel of tinned brass or copper strip material. The tinned metal enters the stamping die and the stamping operation proceeds which cuts out metal traces including at least the active sections from the metal strip and implants them directly onto the hot (newly exited from the mold) insulating material substrate. The assembly (the plastic plus the metal traces) is then indexed out of the die area, and the process then repeats itself with the next segment. The advantages are that the parts coming out of the mold are in a continuous form, and the end result is a simple, low cost plastic substrate housing with the circuit active traces in final form not requiring any further trace separating steps, or at least reducing the number of further trace separating steps that may be required.
In a preferred embodiment, the axial-projecting portion which is used to form the interlocking section or the connecting tabs has a hole or recess for receiving the overmolded part, with the overmolded part helping to lock the previous segment to the next molded segment in a positive manner.
Preferably, the strip if having interlocking sections is provided with severance means, such as notches or score marks, for severing from the strip a discrete length of the material containing one or more components for any of many uses, such as, for example, as part of a package for various items.
The invention is applicable not only to injection molded insulating plastic materials, but also to other similarly formable materials and processes. Typical insulating plastics such as ABS, PPA, polyesters, polypropylene, and polycarbonates can be used to make insulating parts, as well as silicone rubber materials. The formable material can also include fibers for reinforcement, such as glass fibers. Thus, the terms xe2x80x9cmoldedxe2x80x9d, xe2x80x9cinjection-moldedxe2x80x9d, xe2x80x9cmoldablexe2x80x9d, or xe2x80x9cmoldingxe2x80x9d as used herein should be understood in the broadest sense to include not only injection molding of plastics but also of other formable materials.
The semi-continuous molded PCB assembly process described here has many benefits. It""s economical in that the stamped metal traces can be implanted in the insulating material substrate at the same time that the insulating material substrate is molded or at a second stage temporally close to the semi-continuous molding step. It""s also much easier to populate the continuous molded assemblies with components while they are in the continuous reeled form because it eliminates the handling of individual PCBs, and facilitates the automation of the component insertion.
An additional benefit, when the assembly is in continuous form, is that after the boards are populated (while in continuous form) they can be re-reeled, then subsequently automatically inserted into either a plastic housing or into a motherboard. There are many instances when daughter boards are inserted into motherboards (as in radios, TV""s, computers, etc.) and with the assemblies in reeled form then it would be easier to automate their insertion into the housing or the motherboard.
These and other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following descriptions and claims taken in conjunction with the accompanying drawings which illustrate by way of example and not limitation preferred embodiments of the invention and wherein like reference numerals denote like or corresponding parts.